Super Smooth Paper Backing for Fine Grit Abrasives and Methods of Their Application and Use

ABSTRACT

Methods for forming an abrasive backing having a super smooth surface are provided. The method can include applying a bond coating onto a first surface of a saturated, calendered paper; applying a barrier coating onto the bond coating to form an abrasive backing; and calendering the abrasive backing in a heated soft nip calender to produce the super smooth surface on the barrier coating. Abrasive backing sheets and abrasive sheet materials are also generally provided.

BACKGROUND

Abrasive sheet materials are widely used for a variety of applications and include, by way of illustration only, sandpapers, emery cloths, sanding discs for rotary sanders, and sanding strips for orbital and belt sanders. Abrasive sheet materials most often comprise a layer of an abrasive (e.g., abrasive particles or grit), which is attached to a backing substrate of varying thickness and basis weight by means of an adhesive. Typically, a saturated paper is utilized as the backing substrate, leading to the finished product being commonly referred to as “sandpaper.”

The reinforcement of paper by latex polymer impregnation (commonly referred to as latex saturation) is a long-established practice. The polymer employed typically is a synthetic material, most often a latex, and the paper may consist solely of cellulosic fibers or of a mixture of cellulosic and noncellulosic fibers. Polymer reinforcement may be employed to improve one or more of such properties as dimensional stability, resistance to chemical and environmental degradation, resistance to tearing, embossability, resiliency, conformability, moisture and vapor transmission, and abrasion resistance, among others.

Latex polymer barrier coatings may also be used to provide a smooth surface for the application of adhesive and abrasive particles. However, during the drying of latex polymer barrier coatings, small holes can appear in the latex layer. The holes appear due to the release of water vapor during drying and contraction of the dried film during curing. These holes are small, 10-30 microns in average diameter and are referred to as pinholes. Pinholes do not become a problem for fine size grit particles as used in the abrasive industry such as from grit 320 to 600 (35-16 microns in average size). However, in super fine grit applications, i.e., grit 800 to 1200 and finer (12 to 1.2 microns), the presence of pinholes affects the quality of the final abrasive paper product. For example, pinholes can allow super fine particles to become trapped or lodged in the holes. Such trapping of particles can result in a clump of abrasive particles on the final product surface. Such clumping creates an uneven surface that results in poor sanding quality.

Therefore, there exists a need in the art for a super smooth abrasive paper backing that results in improved uniformity of grit particles on the surface thereof and a method of making thereof.

SUMMARY

Objects and advantages of the invention will be set forth in part in the following description, or may be obvious from the description, or may be learned through practice of the invention.

Methods are generally provided for forming an abrasive backing having a super smooth surface. In one embodiment, the method includes applying a bond coating onto a first surface of a saturated, calendered paper; applying a barrier coating onto the bond coating to form an abrasive backing; and calendering the abrasive backing in a heated soft nip calender to produce the super smooth surface on the barrier coating.

Abrasive backing sheets are also generally provided. In one embodiment, the backing sheet includes a saturated paper defining a first surface and a second surface, a bond coating on the first surface of the saturated paper, and a barrier coating on the bond coating. The saturated paper is saturated with a saturant composition comprising a first polymeric binder and a film forming resin. The bond coating comprises a second polymeric binder and a plurality of particles. The barrier coating comprises a third polymeric binder, and the barrier coating defines a surface having a Bekk smoothness of about 1000 sec to about 8000 sec.

Abrasive sheet materials is also generally provided. In one embodiment, the abrasive sheet material includes a backing sheet, such as described above, and an abrasive layer on the barrier coating.

Other features and aspects of the present invention are discussed in greater detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

A full and enabling disclosure of the present invention, including the best mode thereof to one skilled in the art, is set forth more particularly in the remainder of the specification, which includes reference to the accompanying figures, in which:

FIG. 1 shows a cross-sectional view of an exemplary abrasive backing that defines a super smooth surface and includes a saturated paper, a bond coating, and a barrier coating;

FIG. 2 shows a cross-sectional view of an exemplary abrasive sheet material formed from an abrasive backing, such as shown in FIG. 1, with an abrasive layer on the super smooth surface;

FIG. 3 shows a photo micrograph of an exemplary abrasive backing had a super smooth surface on the barrier coating according to the Example; and

FIG. 4 shows a photo micrograph of an abrasive backing made according to a prior method for comparison.

Repeat use of reference characters in the present specification and drawings is intended to represent the same or analogous features or elements of the present invention.

DEFINITIONS

The term “abrasive backing” is used herein to mean a paper, typically a polymer-reinforced paper, which is intended to be provided with a layer of abrasive particles. The term “abrasive paper” refers to the combination of an abrasive backing and a layer of abrasive particles.

As used herein, the term “paper” is meant to include any web or sheet-like material which contains at least about 50 percent by weight of cellulosic fibers. In addition to cellulosic fibers, the web may contain other natural fibers, synthetic fibers, or mixtures thereof. Cellulosic nonwoven webs may be prepared by air laying or wet laying relatively short fibers to form a web or sheet. Thus, the term includes sheets prepared from a papermaking furnish. Such furnish may include only cellulose fibers or a mixture of cellulose fibers with other natural fibers and/or synthetic fibers. The furnish also may contain additives and other materials, such as fillers, e.g., clay and titanium dioxide, surfactants, antifoaming agents, and the like, as is well known in the papermaking art.

As used herein, the term “backside layer” refers to a layer or coating on the backside of an abrasive paper, i.e., the side of the abrasive paper which does not have the layer of abrasive particles thereon.

In the present disclosure, when a layer is being described as “on” or “over” another layer or substrate, it is to be understood that the layers can either be directly contacting each other or have another layer or feature between the layers, unless otherwise stated. Thus, these terms are simply describing the relative position of the layers to each other and do not necessarily mean “on top of” since the relative position above or below depends upon the orientation of the device to the viewer.

The term “organic” is used herein to refer to a class of chemical compounds that are comprised of carbon atoms. For example, an “organic polymer” is a polymer that includes carbon atoms in the polymer backbone.

As used herein, the term “polymer” generally includes, but is not limited to, homopolymers; copolymers, such as, for example, block, graft, random and alternating copolymers; and terpolymers; and blends and modifications thereof. Furthermore, unless otherwise specifically limited, the term “polymer” shall include all possible geometrical configurations of the material. These configurations include, but are not limited to isotactic, syndiotactic, and random symmetries.

As used herein and in the claims, the term “comprising” is inclusive or open-ended and does not exclude additional unrecited elements, compositional components, or method steps. Accordingly, the term “comprising” encompasses the more restrictive terms “consisting essentially of” and “consisting of.”

DETAILED DESCRIPTION

Reference now will be made to the embodiments of the invention, one or more examples of which are set forth below. Each example is provided by way of an explanation of the invention, not as a limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as one embodiment can be used on another embodiment to yield still a further embodiment. Thus, it is intended that the present invention cover such modifications and variations within the scope of the appended claims and their equivalents. It is to be understood by one of ordinary skill in the art that the present discussion is a description of exemplary embodiments only, and is not intended as limiting the broader aspects of the present invention.

An abrasive backing having a super smooth surface is generally provided, along with methods of its formation and use. Referring to FIG. 1, an exemplary embodiment of an abrasive backing 10 is shown. The abrasive backing 10, in this embodiment, includes a saturated paper 12 serving as a base sheet of the abrasive backing 10, and defines a first surface 14 and a second surface 16. A bond coating 20 is positioned on the first surface 14 of the saturated paper 12, and a barrier coating 30 is positioned on the bond coating 20 such that the bond coating 20 is positioned between the saturated paper 12 and the barrier coating 30.

After formation, the abrasive backing 10 defines a super smooth surface 32 for application of an abrasive layer 40 thereon to form an abrasive sheet material 50, as shown in the exemplary embodiment of FIG. 2. The abrasive layer 40 is shown including a plurality of abrasive particles 42 dispersed within an adhesive material 44 on the super smooth surface 32 of the abrasive backing 10. Thus, the abrasive layer 40 defines an abrasive surface 41 of the abrasive sheet material 50.

Each of the components of the abrasive backing 10 and the resulting abrasive sheet material 50 are discussed in greater detail below, along with their methods of formation.

I. Saturated Paper

As stated, the saturated paper 12 used as a base substrate of the abrasive backing 10 and abrasive sheet material 50. Generally, the saturated paper 12 is prepared from a latex-impregnated paper.

In one embodiment, the saturant composition includes a latex polymeric binder, a film forming resin, and optional additional components.

A. Latex Polymeric Binder

As used herein, the term “latex polymer” refers to an emulsion of the polymer in a solvent (typically water). Suitable latex polymeric binder include, but are not limited to polyacrylates, including polymethacrylates, poly(acrylic acid), poly(methacrylic acid), and copolymers of the various acrylate and methacrylate esters and the free acids; styrene-butadiene copolymers; ethylene-vinyl acetate copolymers; nitrile rubbers or acrylonitrile-butadiene copolymers; poly(vinyl chloride); poly(vinyl acetate); ethylene-acrylate copolymers; vinyl acetate-acrylate copolymers; neoprene rubbers or trans-1,4-polychloroprenes; cis-1,4-polyisoprenes; butadiene rubbers or cis- and trans-1,4-polybutadienes; and ethylene-propylene copolymers.

In one embodiment, the latex polymeric binder can include functionalized groups configured to facilitate curing of the latex polymer. For example, latex polymeric binder can include, but are not limited to, carboxyl groups, amine groups, and pyridyl groups. Without wishing to be bound by theory, it is believed that these functionalized groups can facilitate curing of the latex polymer, as well as the crosslinking, by the presence of the polar groups on the latex polymer.

In one particular embodiment, a carboxylated latex polymer is present in the saturant composition. The carboxylated latex polymer can be a copolymer product of the polymerization of a vinyl aromatic monomer and an unsaturated carboxylic acid monomer. The copolymer may further comprise a diene monomer.

Useful vinyl aromatic monomers include, but are not limited to, styrene, alpha-methylstyrene, ethylstyrene, dimethylstyrene, t-butylstyrene, vinylnaphthalene, methoxystyrene, cyanostyrene, acetylstyrene, monochlorostyrene, dichlorostyrene, and other halostyrenes, and mixtures thereof. The vinyl aromatic monomer may be present in any effective amount, such as greater than 0% to about 75% by weight, based on the total weight of the polymer resin. In some embodiments, the vinyl aromatic monomer is present in amounts of from about 35% to about 70% by weight. For example, in one particular embodiment, the vinyl aromatic monomer can be present from about 55% to about 60% by weight.

The ethylenically unsaturated carboxylic acid may be a monocarboxylic acid, or a dicarboxylic acid or a polycarboxylic acid, such as, for example, acrylic acid, methacrylic acid, fumaric acid, maleic acid, itaconic acid, derivatives thereof, and mixtures thereof. The ethylenically unsaturated carboxylic acid monomer may be present in any amount, such as from about 0.5% to about 25% by weight, based on the total weight of the polymeric resin. In one embodiment, the ethylenically unsaturated acid monomer is present in amounts of from about 1% to about 5% by weight, such as from about 3% to about 5% by weight, based on the total weight of the copolymer.

Suitable diene monomers include, but are not limited to, butadiene, isoprene, divinylbenzene, derivatives thereof and mixtures thereof. In one particular embodiment, the diene monomer can be a 1,3-butadiene monomer. When present, the diene monomer may be present from greater than 0% to about 85% by weight, and in one embodiment is present from about 30% to about 65% by weight, based on the total weight of the polymer resin. For instance, in one particular embodiment, the diene monomer can be present from about 40% to about 45% by weight.

The latex polymeric binder may also comprise additional ethylenically unsaturated monomeric components. Specific examples of such ethylenically unsaturated compounds include methyl methacrylate, ethyl acrylate, butyl acrylate, hexyl acrylate, 2-ethylhexyl acrylate, lauryl methacrylate, phenyl acrylate, acrylonitrile, methacrylonitrile, ethyl-chloroacrylate, diethyl maleate, polyglycol maleate, vinyl chloride, vinyl bromide, vinylidene chloride, vinylidene bromide, vinyl methyl ketone, methyl isopropenyl ketone, and vinyl ethyl ester. Derivatives thereof and/or mixtures thereof may be included.

The latex polymeric binder of the saturant composition can have a glass transition temperature (Tg) of less than about 20° C. For example, the glass transition temperature of the latex polymer of the binder composition can be less than about 10° C., such about −5° C. to about 5° C. The glass transition temperature (T_(g)) may be determined by dynamic mechanical analysis (DMA) in accordance with ASTM E1640-09. A Q800 instrument from TA Instruments may be used. The experimental runs may be executed in tension/tension geometry, in a temperature sweep mode in the range from −120° C. to 150° C. with a heating rate of 3° C./min. The strain amplitude frequency may be kept constant (2 Hz) during the test. Three (3) independent samples may be tested to get an average glass transition temperature, which is defined by the peak value of the tan δ curve, wherein tan δ is defined as the ratio of the loss modulus to the storage modulus (tan δ=E″/E′).

In one particular embodiment, a styrene-butadiene latex including carboxyl groups can be included in the saturant composition, such as the carboxylated styrene-butadiene latex sold as DL-240NA by Styron LLC (Berwyn, Pa.), which has a Tg of about 0° C. Without wishing to be bound by theory, carboxylation of the latex polymer is believed to provide polar functional groups along the polymer chain. These polar functional groups can increase the ability of the latex polymer to crosslink upon curing, which can result in a strengthened, bonded polymer matrix formed upon curing.

Additionally, different types of functionalized monomers can be utilized in the same latex polymer. For example, the latex polymer can include both carboxyl groups and pyridyl groups.

The latex polymer can be provided in an emulsion, typically an aqueous emulsion. The solids content of the latex polymer emulsion can be from about 1% by weight to about 65% by weight, such as from about 10% to about 60%. In one particular embodiment, the solids content of the latex polymer emulsion is from about 40% to about 55% by weight.

In most embodiments, the latex polymeric binder is crosslinked upon curing. For example, the latex polymer may be self-crosslinking, without the aid of a crosslinking agent. Alternatively, the latex polymer can be crosslinked to a crosslinking agent, such as a resin.

B. Film Forming Resin

In addition to the latex polymer, a film forming resin can be included in the saturant composition. The film forming resin includes, in one particular embodiment, an styrene maleic anhydride copolymer, which is optionally esterfied. “Styrene maleic anhydride copolymer,” as used herein, means any polymer obtained by copolymerization of one or more maleic anhydride comonomers and of one or more styrene comonomers, the maleic anhydride comonomers optionally being partially or completely hydrolysed. In certain embodiments, the optionally-esterfied styrene maleic anhydride copolymer has styrene and maleic anhydride monomers in a molar ratio of 1:3 to 3:1, more preferably in a molar ratio of 1:2 to 2:1, and more preferably in a molar ratio of about 1:1, including all ranges and subranges therebetween such as 1.2:1 and 1.4:1.

According to particular embodiments, the optionally-esterified styrene maleic anhydride copolymer has a weight-average molecular weight ranging from about 5,000 to 500,000, preferably from about 10,000 to 300,000, and most preferably from about 100,000 to 200,000.

The optionally-esterified styrene maleic anhydride copolymer, in one particular embodiment, has a glass transition temperature (T_(g)) ranging from about 100° C. to 175° C., preferably from about 125° C. to 160° C., and more preferably from about 135° C. to 155° C.

“Esterified styrene maleic anhydride copolymer” as used herein means a styrene maleic anhydride copolymer which has been esterified using a small alcohol compound. Preferably, the small alcohol compound has fewer than 8 carbon atoms, preferably five carbon atoms or fewer. For example, a styrene maleic anhydride copolymer can be esterified via standard esterification techniques using butanol, isobutanol, propanol, isopropanol, ethanol, methanol or any mixture of these alcohols, to produce an esterified styrene maleic anhydride copolymer. Such esterification does not have to be complete. Rather, partial esterification can occur and, in fact, is preferred in accordance with the present invention.

Particularly preferred esterified styrene maleic anhydride copolymers include, but are not limited to, those available from Ashland, Inc. (Covington Ky.) under the Scripset® name. Such commercially available products include solid powder products such as, for example, Scripset® 540, Scripset® 550 and Scripset® 810. An example of a particularly preferred esterified styrene maleic anhydride copolymer is a mixed methyl and isobutyl partial ester sold under the name Scripset® 540. Alternatively, suitable examples of non-esterified styrene maleic anhydride copolymers include, but are not limited to, Ashland, Inc. products Scripset® 520 (styrene/maleic anhydride copolymer).

In accordance with preferred embodiments, the at least one film forming resin is present in the composition in an amount of from about 1% to about 40% by weight based on the dried weight, preferably from about 5% to about 30% by weight, and more preferably from about 10% to about 20% of the total weight of the composition, including all ranges and subranges therebetween, all weights based on the total weight of the composition.

C. Optional Components

Other components can be included in the saturant composition, as desired. For example, a water repellant, such as available under SUNSIZE® 137 (OMNOVA Solutions Inc. in FAIRLAWN, Ohio) and believed to be a stearated melamine resin, can be included. Additionally, an antioxidant compound can be included in the saturant composition. Antioxidants help inhibit oxidation of the saturant composition during the curing process, if cured. Oxidation can discolor the saturant composition and degrade its final physical properties. Examples of antioxidants include, but are not limited to, substituted phenolic compounds such as butylated dihydroxyanisole, di-tert-butyl-p-cresol, and propyl gallate. Additional examples of antioxidants include aromatic amines, such as, di-beta-naphthyl-para-phenylenediamine and phenyl-beta-naphthylamine. If used, the antioxidants may be included in the formulation at a concentration of greater than about 0 parts per one hundred parts solids, based on the weight of the latex polymer. For example, the antioxidants may be included in the saturant composition at a concentration of less than about 10% by weight, preferably, less than about 5%, more preferably, less than about 2%, based on the weight of the latex polymer. In one particular embodiment, a phenol-type antioxidants can be included in the saturant composition, such as the phenol-type antioxidant available under the name Bostex 24 from Akron Dispersions of Akron, Ohio.

Of course, in addition the components identified above, the saturant composition may also include other additives for providing the saturant composition with desirable qualities. Examples include, but are not limited to, chemicals for pH adjustment, surfactants, etc. For example, in one embodiment, ammonia can be present in the saturant composition. Trisodium phosphate can be included in the saturant composition to help control the pH of the emulsion, as an emulsifier, and/or as a thickening agent.

The saturant composition can be applied to the paper backing sheet according to any method, including before, after, or during the paper making process. Preferably, the saturant composition is saturated into the fibrous web after it is formed. Any known saturation technique may be employed, such as brushing, flooded nip saturation, doctor blading, spraying, and direct and offset gravure coating. For example, the web may be exposed to an excess of the solution and then squeezed. The squeezing of excess saturant composition from the web may be accomplished by passing the web between rollers. If desired, the excess binder may be returned to the supply for further use. After squeezing out excess material, the saturated web may then be dried. Other suitable techniques for impregnating a web with a binder composition are described in U.S. Pat. No. 5,595,828 to Weber and U.S. Patent Application Publication No. 2002/0168508 to Reed, et al., which are incorporated herein in their entirety by reference thereto for all purposes. The amount of the saturant composition applied may vary depending on the desired properties of the web, such as the desired permeability.

Typically, the saturant composition is present at an add-on level of from about 10% to about 90%, in some embodiments from about 20% to about 70%, and in some embodiments, from about 30% to about 60%. The add-on level is calculated, on a dry weight basis, by dividing the dry weight of saturant composition applied by the dry weight of the web before treatment, and multiplying the result by 100.

After saturation, the saturated paper can be dried to remove the solvent from the saturant composition. For example, the saturated sheet may be heated to a temperature of at least 100° C., and in some embodiments at least about 150° C., such as at least about 200° C. Suitable drying techniques may include heating with, for example, a conventional oven, microwave, forced air, heated roll, can, thru-air drying, and so forth.

II. Bond Coating

As stated above, a bond coating 20 is applied onto the first surface 14 of the saturated, calendered paper 12. The bond coating 20 can be applied from a bond coating composition that can include, independently, any of the materials discussed above with respect to the saturant composition.

In one embodiment, a latex polymeric binder can included in the bond coating, such as those described above with respect to the saturant composition. Particularly suitable latex polymeric binders are those that adhere or bond well to the first surface 14 of the saturated, calendered paper 12. Particularly suitable latex polymeric binders for the bond coating include, by way of illustration only, polyolefins, especially polyethylene and copolymers of ethylene and one or more of such monomers as vinyl acetate, acrylic acid, methacrylic acid, acrylic acid esters (acrylates), and methacrylic acid esters (methacrylates); copolymers of ethylene with such vinyl monomers as vinyl alcohol, vinyl chloride, and vinylidene chloride; polystyrene and copolymers of styrene with butadiene and acrylonitrile; acrylonitrile-butadiene-styrene terpolymers; polyamides; polyesters, including both homopolymers and copolymers; polyurethanes; and polyether esters. The synthetic latex polymeric binder can be a thermoplastic material or a thermosetting material. One specific example of a suitable latex polymeric binder includes carboxylated styrene-butadiene copolymer latex emulsions, such as the carboxylated styrene-butadiene latex sold as DL-240NA by Styron LLC (Berwyn, Pa.), which has a T_(g) of about 0° C.

Additional materials, such as particles, fillers, emulsifying agents and the like can be included in the bond coating 20, if desired. Suitable particles may include, for instance, silica or silicates, clays, borates, pigments, and the like. Clays may include, without limitation, kaolin minerals (including kaolinite, dickite and nacrite), talc, serpentine minerals, mica minerals (including illite), chlorite minerals, sepiolite, palygorskite, bauxite, etc. Another suitable clay is a smectite type clay. Examples of suitable smectites are, without limitation, montmorillonite (sometimes referred to as bentonite), beidellite, nontronite, hectorite, saponite, sauconite and laponite. Bentonite is an example of a naturally occurring combination of clay particles that are rich in montmorillonite and may also contain other smectites and non-clay mineral constituents. Consequently, montmorillonites or their mixtures with other smectites are often referred to simply as bentonite. Bentonite clays are fine crystals or particles, usually plate-like in shape, with a lateral dimension up to 2 μm and a thickness in a range of a few to tens of nanometers (nm). In one particular embodiment, a pigment can be included in the bond coating, such as titanium oxide, etc.

The inclusion of such particulates within the bond coating can allow control of the adhesive properties and tackiness of the resulting bond coating 20. In particular embodiments, the bond coating 20 can include about 50% 85% by weight of particles based on the dried weight of the final coating, such as about 60% to about 80% by weight.

The thickness of the bond coating 20 can vary according to the intended use for the resulting adhesive backing. For example, a thinner bond coating can be utilized for coarse grit abrasive products, e.g., abrasives having particle sizes of 200 mesh or greater (the term “mesh” is used herein to mean U.S. Standard Sieve mesh). On the other hand, a thicker bond coating may be used for finer grit products which are to be used for polishing or fine surface finishing. A practical minimum layer thickness is about 10 micrometers, whereas the practical maximum layer thickness is about 250 micrometers. However, thinner or thicker layers can be employed, if desired, provided that the layers are continuous. Thermoplastic polymeric compositions which are inherently stiff will be more useful for coarse grit products, while softer or elastomeric thermoplastic polymeric compositions like ethylene-vinyl acetate copolymers and polyurethanes will be more useful for such fine grit products as fine sanding and polishing cloths.

The bond coating can then be dried to remove any liquid solvent (e.g., water) from the resulting coating 20 according to any suitable method, such as those described above.

III. Barrier Coating

Thereafter, the coated paper 12 is coated with a barrier coating 30 that overlays the bond coating 20, and then subjected to a calendering step the abrasive backing in a heated soft nip calender to produce the super smooth surface on the barrier coating

The barrier coating 30 can be applied from a barrier coating composition that can include, independently, any of the materials discussed above with respect to the saturant composition and/or the bond coating composition.

In one embodiment, a latex polymeric binder can be included in the barrier coating, such as those described above with respect to the saturant composition and/or the bond coating. Particularly suitable latex polymeric binders are those that adhere or bond well to the bond coating 20 the saturated, calendered paper 12. For example, one particularly suitable latex polymeric binder for the barrier coating includes an acrylic latex binder. Suitable polyacrylic latex binders can include polymethacrylates, poly(acrylic acid), poly(methacrylic acid), and copolymers of the various acrylate and methacrylate esters and the free acids; ethylene-acrylate copolymers; vinyl acetate-acrylate copolymers, and the like. Suitable acrylic latex polymers that can be utilized as the latex polymeric binder in the barrier coating include those acrylic latexes sold under the trade name HYCAR® by The Lubrizol Corporation (Wickliffe, Ohio), such as HYCAR 26706 acrylic emulsion.

The latex polymeric binders for the saturant composition, the bond coating 20, and the barrier coating 20 can be the same or different. Desirably, the latex polymeric binder of the bond coating adheres or bonds well to the surface 14 of the saturated paper 12, and the latex polymeric binder of the barrier coating flows sufficiently well during subsequent soft nip calendering to fill any pinholes present in the bond coating. For example, latex polymeric binders having viscosities ranging from 30-50 centipoise may be expected to flow sufficiently well to substantially fill any pinholes present in the bond coating. Even more desirably, the latex polymeric binder of the barrier coating is compatible with the particular adhesive which may be used to attach the adhesive particles to the coated surface 32 of the resulting adhesive backing sheet 10.

The thickness of the barrier coating 30 can vary according to the intended use for the resulting adhesive backing. For example, a thinner barrier coating can be utilized for coarse grit abrasive products, e.g., abrasives having particle sizes of 200 mesh or greater (the term “mesh” is used herein to mean U.S. Standard Sieve mesh). On the other hand, a thicker barrier coating may be used for finer grit products which are to be used for polishing or fine surface finishing. A practical minimum layer thickness is about 10 micrometers, whereas the practical maximum layer thickness is about 250 micrometers. However, thinner or thicker layers can be employed, if desired, provided that the layers are continuous. Thermoplastic polymeric compositions which are inherently stiff will be more useful for coarse grit products, while softer or elastomeric thermoplastic polymeric compositions like ethylene-vinyl acetate copolymers and polyurethanes will be more useful for such fine grit products as fine sanding and polishing cloths.

After the bond coating 20 and the barrier coating 30 are applied to the surface 12 of the saturated paper, the coated paper passes through a calender or supercalender to further smooth the surface 32. Specifically, the calendaring process utilizes a soft nip calendar melt and flow the polymeric material of the barrier coating to fill voids in the bond coating and/or the paper surface to form a super smooth surface 32.

For purposes herein, soft nip calendering is carried out at a roll temperature from about 68° F. (about 20° C.) to about 350° F. (about 177° C.) and a calendering pressures from about 100 pounds per linear inch (PLI) (about 18 kg/cm) to about 1700 PLI (about 303 kg/cm). In one embodiment, softer calender rolls, such as fiber-filled rolls, can be used to compress to form a larger contact area in the nip. In one arrangement, the calender nip comprises a steel roll and a soft fiber-filled roll. In another arrangement, for example, a production supercalender stack may include more than two rolls, desirably from about nine to about 11 rolls, stacked upon each other in a vertical arrangement. Desirably the stacked rolls alternate between steel and fiber-filled rolls.

In particular embodiments, the super smooth surface can have a Bekk smoothness of about 1000 sec to about 8000 sec (e.g., about 3500 sec to about 8000 sec, such as about 5000 sec to about 8000 sec). Bekk smoothness is a measure of the time needed to enable a given volume of air to flow between the paper and a surface of glass in contact with the paper (in compliance with ISO standard 5627). The rougher the paper, the more easily air passes via gaps at the surface of the paper (where such gaps are associated with roughness) and the shorter the length of time taken by the air to pass. The smoother the paper, the greater the length of time needed for the air to pass.

IV. Abrasive Layer

The resulting abrasive backing 10 provides a smooth, nonporous surface 32 to which an abrasive coating 40 can be formed to define an abrasive surface 41 of the resulting sandpaper 50. As shown in the embodiment of FIG. 2, the abrasive coating 40 includes abrasive particles 42 dispersed within an adhesive material 44 to define a can be attached, typically by means of an adhesive coating 40.

To attach abrasive particles to the coated surface of the abrasive backing, an adhesive is applied to the smooth, coated surface of the abrasive backing. Any of the known types of adhesives can be used to bond the abrasive particles to the second layer of synthetic polymeric composition. For example, the adhesive may be thermosetting adhesive, such as, by way of illustration only, epoxy resins, epoxy esters, phenolics, polyurethanes, polyesters, and alkyds. Water-based dispersions such as an ammonia-dispersed ethylene-vinyl acetate copolymer also can be employed. The selection of adhesive typically is dictated by the end use, but the adhesive must be compatible with the synthetic polymeric coating over which it is applied. Phenolics are most useful for very tough, coarse abrasive products for rough finishing or shaping, especially where the product needs to be waterproof as well. More flexible adhesives such as epoxy resins and alkyds are also waterproof and are desirable for fine-finishing products. For dry sanding products, animal glues and water based synthetic resins may be used.

Any generally accepted means of applying adhesive to a sheet material can be employed, including such methods as roll, reverse roll, gravure, and Meyer rod coating. It generally is desirable to avoid placing the paper under significant tension in order to minimize paper distortion, especially when the adhesive is being heat cured. Curing temperatures desirably will be kept below about 125° Celsius, as higher temperatures also tend to distort the paper.

In general, any of the commonly employed abrasive materials known to those having ordinary skill in the art can be used. Such materials can vary from very coarse to very fine. Exemplary abrasive materials include silicon carbide, aluminum oxide, garnet, and diamond, by way of illustration only.

In one embodiment, the bonding adhesive may be dissolved or dispersed in a solvent or carrier and the mixture is then applied by a pressure coating nip to the abrasive backing. The abrasive grit particles are then deposited on the moving abrasive backing before the solvent or carrier is driven off, and while the adhesive is still fluid. The grit particles may be oriented or aligned, for example by electrostatic means, to maximize abrasive or cutting properties. Desirably, no external pressure is applied to the particles after deposition, as this may tend to destroy the alignment of particles, or bury the particles in the backing, both of which are undesirable. After the solvent or carrier is driven off, the abrasive backing carrying the adhesive and grit may be passed through an oven which heats the material for times ranging from several minutes to several hours to cure the adhesive and to firmly bond the grit therein.

If desired, one or more layers of an adhesive or other material can be formed over the layer of abrasive particles. Such a layer can serve to better anchor all of the abrasive particles to the abrasive sheet material, thereby reducing abrasive loss during use and increasing the life of the abrasive sheet material.

In general, any of the commonly employed abrasive materials known to those having ordinary skill in the art can be used. Such materials can vary from very coarse to very fine. Exemplary abrasive materials include silicon carbide, aluminum oxide, garnet, and diamond, by way of illustration only.

If desired, one or more layers of an adhesive or other material can be formed over the layer of abrasive particles. Such a layer can serve to better anchor all of the abrasive particles to the abrasive sheet material, thereby reducing abrasive loss during use and increasing the life of the abrasive sheet material. For example, after the grit is firmly bound to the backing, a “grain size” coating may be applied over the layer of abrasive particles. The grain size coating may be a hard, thermosetting resin or animal glue which anchors the particles more firmly so that they remain aligned for maximum cutting ability.

The size of the abrasive particles or grit can be controlled based on the desired sanding or polishing characteristics of the finished product. For example, by utilizing very fine or super fine abrasive materials (e.g., less than 6 microns in average diameter), abrasive sheet materials also can be produced and used for fine sanding and polishing operations.

EXAMPLE

A super smooth abrasive backing was prepared according to the following method. A base paper utilized is available from Neenah Paper, Inc. (Alpharetta, Ga.) under the product code 0248B0, had a basis weigh of 65.8 gsm, and was produced using 4 bales of Alpac Spruce and 0.5 bales of Alpac Aspen.

The paper machine utilized to form the base paper had saturating, calendering, and coating capability. The base paper was formed, and then saturated in-line with a saturant composition according to Table 1. The saturant composition had a pickup of about 23% by weight.

TABLE 1 Saturant Composition Ingredients Solids Parts Dry Wet DL240 48.1% 50 100 207.9 Water 220 Ammonia 3 Scripset 540 (SS58)  9.5% 2 2 21.1 SUNSIZE 137 40.0% 3.5 7 17.5 Totals: 23.2% 109 469.5

Following saturation, the saturated paper was calendered with a steel-on-steel calendar for the formation of uniform caliper.

A bond coating was applied onto a first surface of the saturated, calendered paper, and had a coat weight of 15.0 gsm. The bond coating was applied on the paper machine with the bond coating composition of Table 2.

TABLE 2 Bond Coating Composition Ingredients Solids Parts Dry Wet DL-240NA 48.10% 100 200 415.8 Water 0 356 ULTRAWHITE 69.00% 300 600 869.6 90 Totals: 48.74% 800.0 1641.4

Following drying of the bond coat, a barrier coating was applied onto the bond coat on the saturated, calendered paper, and had a coat weight of 12.0 gsm. The barrier coat was applied onto the bond coat with the barrier coating composition of Table 3.

TABLE 3 Barrier Coating Composition Ingredients Solids Parts Dry Wet Hycar 26706 49.50% 100 200 404.0 Water 0 50 ULTRAWHITE 69.00% 30 60 87.0 90 Totals: 48.06% 260.0 541.0

Thereafter, the abrasive backing was passed through a soft nip calender, with having a roll temperature of 130° C. and a nip pressure of 1200 psig.

The resulting abrasive backing had a super smooth surface on the barrier coating, as shown in FIG. 3. When compared to abrasive backings formed according to the method described in U.S. Pat. No. 7,497,884 of Lindquist, et al. (which is incorporated by reference herein) and shown in the photo micrograph of FIG. 4 disclosed therein, the abrasive backings formed according to the present Example showed a vastly improved surface characteristic in terms of smoothness.

These and other modifications and variations to the present invention may be practiced by those of ordinary skill in the art, without departing from the spirit and scope of the present invention, which is more particularly set forth in the appended claims. In addition, it should be understood the aspects of the various embodiments may be interchanged both in whole or in part. Furthermore, those of ordinary skill in the art will appreciate that the foregoing description is by way of example only, and is not intended to limit the invention so further described in the appended claims. 

What is claimed:
 1. A method of forming an abrasive backing having a super smooth surface, the method comprising: applying a bond coating onto a first surface of a saturated, calendered paper; applying a barrier coating onto the bond coating to form an abrasive backing; and calendering the abrasive backing in a heated soft nip calender to produce the super smooth surface on the barrier coating.
 2. The method of claim 1, further comprising, prior to applying the bond coating: saturating a paper sheet with a saturant composition to form a saturated paper wherein the saturant composition comprises a latex polymeric binder and a film forming resin; and calendering the saturated paper to form the saturated, calendered paper.
 3. The method of claim 2, wherein the latex polymeric binder comprises a carboxylated styrene-butadiene latex.
 4. The method of claim 3, wherein the carboxylated styrene-butadiene latex has a glass transition temperature of about −5° C. to about 5° C.
 5. The method of claim 2, wherein the film forming resin comprises a styrene maleic anhydride copolymer.
 6. The method of claim 5, wherein the styrene maleic anhydride copolymer is an esterfied styrene maleic anhydride copolymer.
 7. The method of claim 1, wherein the bond coating comprises a latex polymeric binder.
 8. The method of claim 7, wherein the latex polymeric binder of the bond coating comprises a carboxylated styrene-butadiene latex.
 9. The method of claim 7, wherein the carboxylated styrene-butadiene latex has a glass transition temperature of about −5° C. to about 5° C.
 10. The method of claim 7, wherein the bond coating further comprises a plurality of particles.
 11. The method of claim 10, wherein the particular comprises a pigment.
 12. The method of claim 1, wherein the barrier coating comprises an acrylic latex binder.
 13. A backing sheet, comprising: a saturated paper defining a first surface and a second surface, wherein the saturated paper is saturated with a saturant composition comprising a first polymeric binder and a film forming resin; a bond coating on the first surface of the saturated paper, wherein the bond coating comprises a second polymeric binder and a plurality of particles; and a barrier coating on the bond coating, wherein the barrier coating comprises a third polymeric binder, wherein the barrier coating defines a surface having a Bekk smoothness of about 1000 sec to about 8000 sec.
 14. The backing sheet of claim 13, wherein the first polymeric binder comprises a carboxylated styrene-butadiene latex.
 15. The backing sheet of claim 14, wherein the second polymeric binder comprises a carboxylated styrene-butadiene latex.
 16. The backing sheet of claim 15, wherein the third polymeric binder comprises an acrylic binder.
 17. The backing sheet of claim 16, wherein the plurality of particles comprises a pigment.
 18. An abrasive sheet material, comprising: a saturated paper defining a first surface and a second surface, wherein the saturant composition comprises a first polymeric binder and a film forming resin; a bond coating on the first surface of the saturated paper, wherein the bond coating comprises a second polymeric binder and a plurality of particles; a barrier coating on the bond coating, wherein the barrier coating comprises a third polymeric binder, wherein the barrier coating defines a surface having a Bekk smoothness of about 1000 sec to about 8000 sec; and an abrasive layer on the barrier coating. 